An empty Greyhound bus was swiped from a garage in Manhattan, finally showing up abandoned in Queens yesterday.

But officials have no idea who took the bus — or when it actually went missing.

A driver for the rival Peter Pan bus company spotted the vehicle on Astoria Boulevard and alerted Greyhound at around 2:15 a.m., a source said.

Greyhound promptly sent out a mechanic from the 12th Avenue garage.

But the mechanic didn’t find the bus where the crew sent him and called cops, who finally located the missing vehicle at Astoria Boulevard and 29th Avenue at 12:45 p.m., the source said

The bus had been taken to the West Side garage Feb. 14 for routine maintenance.

Cops yesterday pored over surveillance video from the garage. Sources said investigators think the caper may have been an inside job, since the thief apparently knew how to get access to the bus battery and disable it in Queens.

“We’re working with local law enforcement,” said Greyhound spokeswoman Maureen Richmond.